Field of the Invention
The present invention relates to a light scanning apparatus including a rotary polygon mirror, to an image forming apparatus including the light scanning apparatus, and to a method of manufacturing the light scanning apparatus.
Description of the Related Art
Hitherto, an electrophotographic image forming apparatus includes a light scanning apparatus. The light scanning apparatus is configured to deflect a light beam emitted from a light source with the use of a rotary polygon mirror. The deflected light beam is scanned on a photosensitive drum through an fθ lens, to thereby form an electrostatic latent image.
The image forming apparatus needs to determine an emitting start timing of a light beam in order to keep a writing start position of an image at a fixed position in a main scanning direction. In order to determine the emitting start timing of the light beam, the light scanning apparatus generally includes a light beam detector (hereinafter referred to as “BD”). The BD is configured to output a BD signal when the BD receives the light beam emitted from the light source and deflected by the rotary polygon mirror. The image forming apparatus is configured to determine the emitting start timing of the light beam based on the BD signal. However, in order to enable the BD to generate the BD signal, optical components such as a condeser lens and a slit configured to allow the light beam to enter the BD are required in addition to the BD. Therefore, there arises a problem in that the number of components and the assembly man-hours are increased, to thereby raise the cost.
In the aim of solving this problem, there is disclosed in U.S. Pat. No. 7,345,695 that the emitting start timing of the light beam is determined, without use of the BD, by detecting a reference mark arranged on the rotary polygon mirror or on a member integrally rotated with the rotary polygon mirror.
However, the arrangement of the reference mark and a detector configured to detect the reference mark still poses the problem in that the number of components and the assembly man-hours are increased, to thereby raise the cost.